bibexport – Extract a BibTeX file based on a .aux file

A Bourne shell script that uses BibTeX to ex­tract bib­li­og­ra­phy en­tries
that are \cite'd in a doc­u­ment. It can also ex­pand a BibTeX file,
ex­pand­ing the ab­bre­vi­a­tions (other than the built-in ones like
month names) and fol­low­ing the cross-ref­er­ences.